Conventional actinometers employed in testing apparatus for measuring light fastness or weather-resistance employ silicon photocells as the light-receiving portions, and a photocurrent corresponding to the magnitude of light energy impinging on the photocells is fed to the electrolytic cell which is used to determine the total energy by determining the amount of mercury precipitated on the cathode due to the electrolysis of mercury iodide in the electrolyte by the photocurrent.
FIG. 1 shows the construction of a conventional electrolytic cell in which a separator wall 3 constituted by a glass filter is positioned in the upper central portion of a glass vessel 1, mercury 4 is stored in the lower portion on one side of the wall 2, and a tube 5 stretches downward from the bottom of the other side and contains an electrolyte 6 and precipitated mercury 7. On the one side of the glass vessel 1, the electrolyte and mercury are in upper and lower layers and a platinum wire 8 extends into the lower mercury layer to form an anode. On the other side of the glass vessel 1 a platinum wire 9 extends into the electrolyte to form a cathode 10. The other ends of the platinum wires are connected to a light-receiving unit. Although the sensitivity is low, the above conventional actinometer can make satisfactory measurements if used over an extended period of time. For example, when the energy radiated from a carbon arc lamp, used as a light source for light-fastness and weather-resistance testers, is measured, the actinometer is mounted on a specimen rack of the tester and rotated around the light source. After the light has been received for one week, the precipitated mercury 7 will have a depth of about 7 mm. When the light is received for one month, the precipitated mercury 7 will have a depth of about 30 mm. Depending upon the depth, therefore, the total amount of energy received can be determined.
Up to now such an actinometer has been used as an indicating means for, when the intensity of the source of light as measured by the actinometer deviates from the specified energy values, indicating that the lamp which acts as the light source should be checked and adjusted so that the intensity of light falls within a specified range.
When the measurement is carried out with a conventional actinometer for only one day, however, the depth of the precipitated mercury is less than 1 mm, and it is very difficult to obtain accurate results from such a small depth of mercury.
At present, however, the need to increase the precision of measurements and to save power have created increasing demands for the development of electrolytic cells capable of performing a similar measurement in less than one day.